It is well-known that acids are formed during the oxidation of hydrocarbons such as isobutane, by the decomposition of peroxides such as t-butylhydroperoxide in crude tertiary butyl alcohol (tBA) feed, and from the hydrolysis of formates present in the tBA feed, resulting in the presence of acids such as, for example, formic acid, acetic acid, and isobutyric acid in the feed to a one-step process for making MTBE. In MTBE pilot plants where carbon steel is sometimes used in the one-step reactor and distillation towers, these acids have been shown to cause significant corrosion if left untreated.
One solution to this problem is sodium hydroxide injection into the effluent stream of the MTBE one-step reactor in order to neutralize said acids, however this solution may lead to unacceptable corrosion rates certain points in the process. In addition, the injection of caustic poses other concerns such as potential foaming in downstream distillation columns, formation of a second liquid phase with the additional water introduced with the caustic, and the necessity to control pH, which is notoriously difficult.
U.S. Pat. No. 5,106,458 discloses a process for removing methyl formate from impure propylene oxide which comprises contacting said impure propylene oxide in a treating zone with a strongly basic ion exchange resin for a period of time sufficient to convert said methyl formate to formic acid and methanol. The preferred basic ion exchange resin is a styrene divinylbenzene copolymer containing quaternary ammonium groups.
One reference in the art which addresses the topics of adsorption and ion exchange is Perry, R. H. and Green, D. W., Perry's Chemical Engineer's Handbook, 6th Ed., Sec. 16, McGraw-Hill, 1984. This text includes an analysis of design strategies for various fixed-bed separations.
Another reference recognized in the art is Schweitzer, P. A., Handbook of Separation Techniques for Chemical Engineers, p. 387, McGraw-Hill, 1979. Section 1.12, by Robert Anderson, includes a very good overview of the factors involved in a resin system.
From a survey of references available in the art, it would appear that the accepted method of attempting to remove formic acid and other organic acids from the effluent of a one-step process for producing MTBE is the previously mentioned injection of sodium hydroxide into the stream, however, it is apparent that method can cause problems downstream, as well as other disadvantages.
It would represent a distinct advance in the art if there were a method available for treating MTBE effluent streams which did not contribute to corrosion. It would represent an advance over any method known presently in the art if the formic acid, methyl formate and butyl formate could be removed from an MTBE effluent stream in a manner which did not contribute to problems such as foaming in downstream distillation columns, formation of a second liquid phase with the addition of water introduced with the caustic, and the necessity to control pH.